The present invention relates to conveyors, and, in particular, to a conveyor which is driven by a line shaft and which is divided into zones, such that the zones can be selectively driven or stopped.
There are many situations in which an accumulation conveyor is needed. For instance, if there is a blockage or a back-up in the conveyor line, articles can begin to bump into each other, with the line pressure increasing as the number of articles pushing on the front-most article increases, so that the articles in the front of the blockage tend to be crushed and damaged. When an accumulation conveyor is available in that situation, it senses the blockage or back-up, and the zones leading up to the blockage stop being driven as articles arrive in them, so that articles are accumulated on the conveyor without crushing each other. When the blockage is removed, the zones again begin driving, in order to convey the articles along their intended path.
Line shaft driven conveyors are very popular, because they require only a single drive for the entire conveyor, and a good accumulation arrangement for this type of conveyor is needed. U.S. Pat. No. 4,819,788 "Van Der Schie" shows a line shaft type of conveyor which has been adapted to function as an accumulation conveyor. In the Van Der Schie patent, a plurality of tubes surround the drive shaft. The tubes are normally driven along with the drive shaft, due to friction between the tube and the drive shaft. Each tube has a plurality of O-rings wrapped around it, with each O-ring also being wrapped around its respective roller. The group of rollers driven by any given tube defines a zone. Under normal conditions, when the drive shaft rotates, the tubes rotate, causing the O-rings to drive their rollers. However, if accumulation is desired, a brake is applied to the tube of the zone for which driving is to be stopped. Then, the drive shaft continues to rotate, but the brake prevents the respective tube from rotating with the drive shaft.
This arrangement wastes energy, because the drive shaft is trying to drive the tubes all the time, even when the tubes do not rotate. In addition, the wasted energy becomes heat, which must be dissipated somewhere in the conveyor. Also, the continuous friction between the parts tends to make the parts wear out.
Another problem with the Van Der Schie design is that, when one of the O-rings breaks and has to be replaced, it is necessary to disconnect the entire drive shaft, slide the new O-ring over the drive shaft, and then realign all the drive shaft pieces again. This means that considerable maintenance work is required to keep the conveyor operating, and it means that there will be a considerable amount of down-time for the conveyor. When a conveyor is shut down, it may cause an entire manufacturing or distribution process to shut down, so minimizing the amount of down-time for maintenance can be a tremendous cost savings.